1. Field of the Invention
This invention relates to anti-vibration, isolation devices for machines, in particular elastic mountings for automobile motors or the cabs of large trucks. It relates to high-flexibility mountings with integrated hydraulic damping, increasing the apparent rigidity in a very limited range of rather low frequencies, by means of a column of liquid which is very long in relation to its cross section. The resonance of this column counteracts large amplitude displacements, but does not deleteriously affect, to any substantial degree, the elastic filtering a higher frequencies.
A range of such elastic mountings is generally made possible by means of a thick conical elastomer membrane which, when bonded to a support casing and a central framework to fasten it to the housing to be suspended, e.g., the power unit, encloses a chamber containing a damping liquid forced into an expansion space, under low pressure, through a device with a long inertial column, with the major portion of the vertical load being borne by deformation of the elastomer constituting the conical membrane.
French Patent Nos. 2,443,615, 2,462,618, 2,467,724 and 2,511,105 (Peugeot) describe devices which fit this definition and which have the advantage of being integratable into the elastic apparatus with a damping column, which is fitted in a rigid wall immersed in the hydraulic circuit. Thus constituted, the device after being sealed, e.g., by crimping on an attachment cover for the casing, of the mounting, thereby manifests itself as a one-piece component.
Various improvements have been made to these devices. For example, the device based on a hydrodynamic braking nozzle (French Patent No. 2,430,546 to Chrysler) includes a displacement of liquid aided by a resonant mass, acting as an inertial damper Others relate to the use of the mass of the liquid itself, and an adjustment of the characteristics thereof, thereby making possible a low rigidity in response to vibrations at frequencies higher than 25 Hz. Low rigidity in this frequency range is effective for general soundproofing, and also provides good damping at the suspension frequencies, that is, in the range of 5 to 15 Hz, where disturbances become noticeable to passengers, as soon as the amplitude of the movements communicated to the supported structure exceeds one millimeter.
French Patent No. 2,575,253 for this type of hydraulic shock absorber, called a "column mounting", specifies the simultaneous existence of a secondary passage having different throttling characteristics than the principal throttling passage.
An analysis of the prior art shows that it apparently does not include hydroelastic mountings with a long liquid column which is possibly even longer than the length of an annular passage and which passage can easily be adjusted to accommodate the hydroelastic mounting.
All of the above-mentioned patents are hereby expressly incorporated by reference as if the entire contents thereof were fully set forth herein.
2. Object of the Invention
The object of the invention is to provide a hydroelastic mounting with a structure having a passage for receiving the damping liquid, which passage is housed in the rigid partition between the variable volume chamber and the expansion space of a hydroelastic mounting. The length and/or cross section of this passage can be adjusted to substantially, precisely regulate the strokes and frequencies necessary for use in particular applications, by acting on the mass of liquid contained in this passage and on the surface of the boundary layer sheared during the alternating movements of the liquid.